This invention relates to a liquid level control system, and more particularly, to a boiler water level control system having a liquid level adjuster connected to the boiler by conduits, and film membranes positioned between the boiler and the conduits to transmit fluid pressure to the liquid level adjuster while preventing the passage of sludge, corrosive chemicals and other foreign matter from the boiler into the liquid level control system.
Water level control systems for boilers customarily include fluid pressure measuring instruments and conduits connecting the fluid pressure measuring instruments to the boiler. The fluid pressure measuring instruments operate a feedwater control valve which allows water to flow into the boiler to replace the water that leaves as steam. Corrosive chemicals which are present in the boiler water tend to corrode the conduits and the measuring instruments, and sludge which builds up in the boiler also builds up in the water level control system, clogging up both the instruments and the conduits connecting the instruments to the boiler, thereby rendering the system inoperative.
In the past, attempts were made to prevent the fouling due to the sludge by providing sludge pots for the control system and periodically blowing them down. During blowdown, water is allowed to rush out through the pots so that it loosens any sludge and carries it out of the pots. The provision of sludge pots has failed to prevent sludge from entering the control system, and the blowdown procedure is both inconvenient and costly. Furthermore, the entry of the corrosive chemicals into the control system from the boiler and the resultant damage to the conduits and the instruments has been unaffected by the use of sludge pots.